Sunlight is one of the blessings of nature that humankind takes for granted. Sunlight is, in fact, the basic component from which all life originates, develops, heals, and evolves.
The simple fact that we decide when is day and when is night based on the availability of sunlight is the most obvious and significant, yet overlooked effect of sunlight on our lives.
Effect on the human body
The human body clock depends on circadian rhythms, or twenty-four hour cycles of light and darkness. These rhythms are light sensitive, depending on the light that enters the body. Inadequate sunlight affects these rhythms and impairs the body's ability to function properly.
The availability of sunlight triggers an overall feel-good atmosphere for most people. This is because sunlight stimulates production of brain chemical serotonin. Serotonin controls sleep patters, body temperature and sex drive. Lack of sufficient sunlight and thereby less serotonin is enough reason for people to fall into depression, especially Seasonal Affective Disorder (SAD).
Sunlight also triggers the body to make its own vitamin D, which is crucial to health. Vitamin D increases the oxygen-count in the blood and results in increased energy, sharp minds, strong bones, and healthy teeth. Dietary intake provides for only about a quarter of the required amount of Vitamin-D. The rest has to come from exposure to sunlight.
The ultra-violet rays of sunlight helps in breaking down cholesterol, which at high levels damages the lining of arteries and cause serious heart disease.
However too much of a good thing is also bad. Over exposure to sunlight runs the risk of skin cancer, and looking directly at the sun can cause long-term vision damage.
Effect on growth of civilization
The influence on sunlight in our lives is however, not limited to the effect on human body.Humans have, since ages harnessed sunlight to grow and further the cause of civilization.
Plants use the energy of sunlight for photosynthesis that is turning air into simple sugars. Organisms then use these sugars as building blocks to grow. When animals consume these plants in order to sustain or grow, they thus use light from the sun indirectly.
When animals consume plants, the sugars and other molecular components produced by the plants using sunlight are broken down. This releases the stored solar energy in them, and gives the animal the energy required for survival. When human beings consume plants or animals, the process repeats itself.
During the Neolithic Revolution in history, humans gained more access to solar energy in such a fashion by domestication of plants and animals. The more recent discoveries of coal, petroleum, and natural gas are modern extensions of this trend. These fossil fuels are the remnants of ancient plant and animal matter, formed using energy from sunlight and then trapped within the earth for millions of years.
Effect on climate:
The climate of the earth and the different seasons depend on the availability of sunlight. About half of the light given out by the sun is infrared radiations, absorbed by the air. By absorbing this infrared radiation, air heats up, expands and rise, and forms thermal currents. These thermal currents directly affect weather conditions on the planet.
Sunlight causes water to evaporate from rivers, seas, and green plants. The atmosphere either retains this evaporated water as clouds, or sends them back to the earth as rain or snow. This has an affect on the climate as well.
The passing of days and night, from the light of the sun to the darkness, are all aspects of the wonders of creation. If man thinks deep enough, he would realize that sunlight is one of the marvels of the universe and a bounty offered by nature.
Jacob Liberman, "Light: Medicine of the Future: How We can use it to Heal Ourselves now."
adsabs.harvard.edu/abs/1966Natur.212...19V - by A Vecht 1966
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